Question: 4 erasers cost $6.56. Which equation would help determine the cost of 12 erasers?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 4 erasers. We want to know the cost of 12 erasers. We can write the numbers of erasers as a proportion: $\dfrac{4}{12}$ We know 4 erasers costs $6.56. We can let $x$ represent the unknown cost of 12 erasers. The proportion of these costs can be expressed as: $\dfrac{\$6.56}{x}$ The cost changes along with the number of erasers purchased, and so the two proportions are equivalent. $\dfrac{4}{12} = \dfrac{\$6.56}{x}$